1. Field of the Invention
This invention relates to technologies for controlling power consumption in portable or battery-powered devices which perform a function of wireless networking or communications, including but not limited to battery consumption optimization for handheld computers with wireless network interfaces, cordless telephones, cellular telephones, and specialized portable terminal devices (e.g. handheld bar coding equipment, portable point-of-sale devices, etc.)
2. Background of the Invention
Battery-powered, portable devices which perform wireless networking for voice and/or data communications as all or part of their functionality are well known in the art, including but not limited to:                (a) cellular telephones;        (b) wireless web browsers;        (c) cordless telephones and cordless small office/home office (SOHO) telephone switch systems;        (d) laptop computers, palm top computers and personal digital assistants (PDA) equipped with wireless local area network (LAN) or cellular data interface cards;        (e) handheld system terminals such as the units used by car rental companies to check in cars upon their return;        (f) handheld bar code and inventory terminals such as those used by retail and warehousing enterprises;        (g) wireless point-of-sale (POS) terminals such as price scanners and cash registers; and        (h) one-way, two-way, text and voice pagers and terminal devices.        
All of these devices have several architectural aspects in common. First, they are primarily battery powered between periods of recharging. Recharging of the battery may occur when the device is placed in a cradle, attached to the docking station, or plugged into the battery charger device. They each must manage battery consumption efficiently, as battery life is a key factor for selection of a device in a highly competitive industry. For larger systems such as laptop computers, this may include shutting down disk drives under certain conditions. For most systems, this also includes turning off display backlights, shutting dawn or suspending non-critical software and hardware functions, to completing powering down the entire unit.
It is common within the industry to refer to these various methods of battery consumption as “standby”, “sleep”, “suspension”, “battery saver”, or “low power” mode. Although almost all battery-powered devices such as these advertise and claim “advanced” battery saving functions, most implement different schemes of power consumption management depending on their specific control firmware and the hardware capabilities of the system to shut down or sleep portions of the system. So, even though two comparable personal communications systems (PCS) telephones use the same battery type, such as a Lithium Ion battery, and have the same wireless range, their operational characteristics may be considerably different based upon their ability to disable or control power consumption.
For the remainder of this description, we will refer primarily to cellular telephone examples and implementations. Certain terms from cellular telephone parlance are analogous in functionality to terms from other networking technologies, such as PCS towers being similar to “base stations” or wireless access points. It will be readily recognized by those skilled in the art, however, that the problems and the invention presented herein are common to all the various wireless network battery-powered devices as previously exemplified.
Turning to FIG. 1, two “cells” (10, 11) are shown geographically adjacent to each other, each cell having a “tower” (12, 13) located in its center. In this example, the cells are considered to be of hexagonal shape (15, 17) for network planning and management purposes, but in reality, the signals from the towers propagate equally well for a generally circular area (14, 16) of coverage, barring any geophysical obstruction such as a mountain, bluff, or tall building. The hexagonal cells fit wholly within the circular regions around each tower, thereby producing areas of coverage overlap (18) between adjacent cells. In practice, a cellular system (19) comprises multiple cells in a honeycomb arrangement, but only two adjacent cells are shown here for ease of understanding.
When a terminal device such as PCS handset or wireless web browser is at a position P1 outside of reception range of a tower within the system, the device will be unable to perform its functions such as making or receiving telephone calls, performing data communications, etc. Most systems will continuously “search” for a tower signal, performing some type of protocol to make contact with one or more towers which may be within reception range. This process of searching may simply include measuring a signal strength on a frequency and/or channel from the tower, or may be more active such as sending or transmitting a signal from the device's transmitter to initiate a contact with an in-range tower. While the former approach will consume some power for the search, the latter almost always consumes even more power as transmission of signals is usually a more power intensive operation than simply receiving a signal.
As a device reaches or travels a position to the “fringe” area of coverage for a tower P2, it may detect a usable signal strength from the tower (12) within its reception range, and/or may be able to effectively transmit a code, registration or other signal to the tower (12). At this position, the device is technically within the tower's cell (10).
The “logging in” or “registration” process as a device enters a tower's cell varies between different wireless technologies. For example, the registration process employed by PCS systems is different than the registration process used by its predecessor “analog” (e.g. AMPS”) cellular system, and both are very different than the registration process employed by wireless data networking technologies such as BlueTooth, IEEE 802.11b, Motorola's Ricochet network, two-way pager networks, etc. For illustrative purposes, however, we now present a brief overview of the PCS registration process.
When a PCS telephone is first turned ON, it begins to “listen” for or search for a System Identification (SID) code which is continuously transmitted by PCS towers on a predetermined “control channel” frequency. Each PCS system operator (e.g. Sprint, MCI, AT&T, Verizon, VoiceStream, etc.) has been assigned a unique SID value, such that a PCS phone can determine if it is within a network compatible with and authorized for its use. Until a compatible SID code is received, the PCS handset will display a “No Service” indicator or “Out of Range” indicator.
Once the handset has received a compatible SID, it transmits a registration request with the SID on the control channel, which is received by one or more towers within range. For example, in FIG. 1, if the handset is in position P2, only one tower (12) may receive the registration request. If the handset is in position P4, however, when it is powered ON initially, it may be within the overlap of multiple cells, and the registration request may be received by multiple towers (12, 13), or may be directed to the tower for which the strongest signal strength is detected.
Many wireless networked systems are designed to handle providing continuous service as a unit travels from one cell to another, while other technologies do not provide this functionality. For example, a PCS telephone is expected to be used in a moving vehicle or while walking, and as such, the PCS system specifications and design include protocols and schemes for “hand off” of service to a handset from one cell tower to another. So, for example, as a handset moves from position P3 to position P4, and then to position P5, the handset may initially be served by first tower (12) and then be handed off to another tower (13) according to signal strength criteria and channel availability in each area of coverage (14, 16).
Turning to FIG. 2, a larger portion of a cellular network (24) is illustrated, to show how a terminal or handset may traverse multiple positions P1, P2, P3, P4, P5, P6, P7, and P8, starting outside a network, entering the fringe of the network, passing through and being served by multiple cells (20, 21), and finally passing through the fringe and out of the network. Certain cells (23, 22) may never provide service to the handset based upon its position and proximity to other, closer towers.
If a handset, however, moves around the “fringe” area of a network or near the extremes of range for tower or base station, such as moving back and forth between positions P1 and P2 or positions P7 and P8, the handset may repeatedly lose service, reregister, etc. This problem may arise when a handset is located clearly within the geographic region of a cell, cut in an area where reception is attenuated by geographical features of man-made structures such as buildings. For example, as shown in FIG. 3, assume a handset is located within the normal cell range of a tower (34) inside a building (31), the building having several outside wall portions (33) which highly attenuate (35′, 35′) the signal (35) from the tower (34). Additionally, the building may have doors and/or windows (32) which do not cause considerable attenuation (35″)” of the signal (35) from tower (34).
Within the building, false “fringe” areas may be created, shown by the dotted lines, due to the inconsistent signal attenuation of building parts such that as a handset moves from position P1 to position P2 and then to position P3, the signal may be lost and found intermittently. This may cause the handset to have to reregister repeatedly as in the case of moving in and out of geographic service areas, although the cause of the problem is due to signal obstruction rather than geographic range.
A similar problem may also arise as environmental conditions change, such as weather and/or electromagnetic interference (e.g. sun spot activity), causing a signal to “fade in and out”.
Some technologies, however, assume that the terminals are relatively stationary, such as the PCS-derivative wireless local loop (WLL), and some wireless data networking technologies such as “WiFi”. These systems do not include the hardware and software functionalities to perform the “hand off” from one tower, base station or access point, on the assumption that the terminals will remain within range of a selected tower for the duration of the operation of the unit.
To save battery consumption, many methods and systems have been devised implemented in part in hardware or “silicon” solutions, and in part in software and firmware. Or example, most terminals will turn off high-consumption functions such as display and keyboard backlights after a period of inactivity, regardless of network signal strength. Still more power is saved when the system has been out of range of a tower or base station for a given period of time. The terminal or handset will go into “sleep” mode for a predetermined amount of time in which it powers down nonessential portions of the handset, wake up when the sleep period has transpired, and begin the process again. Most of the timer schemes found in current handsets and terminals are relatively simple, although some more advanced approaches are available.
Turning to FIG. 6, an illustration (60) of such a common battery saving scheme is given. As the signal strength (61) varies, the mode (62) of the terminal will vary as will the power consumption (63). In this example, when the terminal is initially switched from OFF to ON, it enters a period of searching for a tower (or base station). Because the signal strength is initially strong, service is initiated (“found”), and battery consumption is normal (C2). Later, however, as the signal strength fades, the terminal enters a period T1. During which it searches for another tower for service. After the tower is not found for this amount of time, it will enter a lower power “sleep” state for a predetermined period T2. During this sleep period, the signal strength may temporary improve, and fade again.
When the sleep time T2 expires, the terminal “wakes up”, returning to a normal battery consumption level, white it searches and reregisters with the closest available tower, assuming signal strength is good as shown in this example. However, if the signal strength fades again soon, as is common intermittent conditions (e.g. inside buildings, transient weather, etc.), the terminal again will spend period T1 searching for a usable tower signal before it returns to sleep. This causes a waster of battery energy (C1). For many wireless terminals and devices, battery consumption during the “search for signal” mode is much higher than idle mode while a signal is available. For example, in an office where “false positives” or intermittent signal acquisitions are made all day, a user's phone is basically in search mode all day long. In such a situation, the phone battery is often dead by the end of the day, in contrast to a day of use outside the office in range of a normal signal during which the battery may last two days or more on a signal charge.
FIG. 5 provides a logical process (50) depiction for this type of battery saving method, including registering (52) initially with a first tower after searching (51) and finding the first tower's signal, losing (53) the signal from the first tower, searching (53) for a valid signal for a predetermined period T1, and then iteratively sleeping (54) for a predetermined period T2 and waking to search (55) until a valid signal is found (57) and the unit can register (58) with the same or an alternate tower.
Intermittent signal conditions such as there, unfortunately, are very common when a handset is present in conditions such as previously described. Additionally, as the handset is automated for these types of operations, many users may be completely unaware that their handset is performing transitory operations, especially if the handset provides no indication (e.g. a beep or tone) that signal is being found, lost found, lost, etc. So many users of such wireless devices experience much shorter battery life than advertised, but are unaware of the cause or potential remedies for the situation.
Manual remedies may include turning OFF the device when entering an area of known conditions such as this. This, however, is counterintuitive to using the device continuously, and depends in a great part on the knowledge and foresight of the user about such geographic and environmental conditions. For example, a user would have to:                (a) know that his office is near the fringe of signal strength;        (b) notice that a strong storm is arriving in the area;        (c) have the presence of mind to turn OFF the device at the storm's outset; and        (d) have the presence of mind to turn it back ON again when the storm has passed.        
This process would likely lead to not turning the handset back ON, missed calls, etc. Alternatively, the user could take the PCS handset OFF his belt clip or out of her purse when in a building known to cause these problems, place the unit near a window during their visit to the building, and retrieve the unit before leaving. This would likely lead to missed calls (e.g. user is in another room when the phone rings), and lost handsets (e.g. user forgets to take his or her phone with them when they leave).
Therefore, there is a need in the art for a system and method which intelligently minimizes the battery consumption of portable or mobile wireless devices. Preferably, this new system and method would achieve such battery savings and life extension without expensive or complex additional circuitry or technology than is typically present in such wireless devices.